Imaging of organs is a technique that utilizes a compound that is active in the body and which has been tagged with a radioactive element which can be detected using a special camera, the type camera being dependent upon the type of emissions from the radioactive element. This diagnostic tool is useful in studying reactions that take place in various body organs and can provide early detection of unusual reactions that can be indicative of disease. The chemical compound that carries the radioactive tag or label must travel through the organ that is being studied and must undergo a reaction that will provide information related to the state of health of the organ or the presence of a tumor. Glucose is the primary energy source of the brain and is also an important metabolic substrate for a normal heart and is therefore a good choice when selecting a vehicle to be tagged.
In the search for a suitable radiopharmaceutical for imaging purposes fluorine-18 has been used as a tag to form the compound fluoro-2-deoxy-D-glucose. Although the tagged compound is easily synthesized, fluorine-18 is available only from a cyclotron or reactor and it has a half-life of only 110 minutes; therefore, it is not readily available and its emissions are of limited duration. In addition to these problems, it also emits positrons having 511 keV gamma rays which cannot be detected using commonly available cameras. Considering their short half-lives, these compounds cannot be stored so they must be made, used, and measured at a single location, and since most hospitals do not have cyclotrons, reactors or special cameras for detecting the fluorine-18 compounds, this compound is not a practical choice for diagnostic purposes on a large scale. Another radioactive element, carbon-11, also would be easily incorporated into a glucose molecule; however, its half-life is only 20 minutes and it also emits 511 keV positrons.
A better choice is iodine-123 which emits particles having 159 keV that can be detected by all nuclear medicine imaging cameras, and since it also has a half-life of 13.3 hours, it can be stored for a longer period of time than can radioactive fluorine or carbon. However, use of iodine presents a problem because, due to its chemical properties, iodine is not easily attached to glucose or a glucose-like molecule. Therefore, there is a need to develop a process to synthesize iodine-123 tagged compounds which undergo reaction in desired organs or tumors in the body.